Generally, an electrophotographic image forming process or an electrostatic printing process includes the steps of (1) forming an electro-conductive image (i.e., a latent image) or an electrostatically charged image corresponding to a recorded image on the surface of an electrostatic recording medium, for example, an OPC (Organic Photo-conductor) drum, (2) developing the latent image with a charged toner, (3) transferring the developed toner image onto a recording material, such as a paper or a recordable film, and (4) fixing the transferred image on the recording material with a heat-compressing roller. The image-forming process such as the electrophotographic image forming process or the electrostatic printing process has advantages in that a printed or copied matter can be obtained with a high speed, the image formed on a recording material is stable, and an image-forming device is easy to manipulate. Therefore, the image-forming process has been widely used in the fields of copiers and printers.
The toner for the developing process can be classified into a one-component toner, a two-component toner, etc. The two-component toner includes a binder resin, a coloring agent, an electrification control agent, various additives, and magnetic substances for developing the latent image formed on a drum and transferring the developed image. In general, the toner is produced in the form of particles by melting, kneading, and dispersing the toner components, and then finely pulverizing and classifying the kneaded components. The binder resin, which is one of the main components of the toner composition, should have desirable properties in dispersing the coloring agent, and in a fixing property, an offset-preventing property, a storage-stability, and an electrical property. The binder resin also should have a good transparency, and produce a clear image even when a small amount of the coloring agent is used. Further preferably, the binder resin should have a wide color expression range, improve the image density of a copied or printed image, and be environmentally desirable.
As the binder resin, polystyrene resin, styrene-acrylic resin, epoxy resin, and polyamide resin have been conventionally used. Recently, a polyester resin is more commonly used as the binder resin due to its superior fixing property, good transparency, and so on. Also, a wax is generally added to the toner to improve offset-preventing property of the toner. However, the compatibility of the wax and the polyester resin is not good, and the wax can not be uniformly mixed with the polyester resin in the toner. To resolve this problem, Korean Patent Laid Open No. 10-2004-0010752 discloses a polyester resin polymerized in the presence of Carnauba wax consisting of aliphatic ester, aliphatic acid and alcohol. However, in this case, the wax can be deteriorated, carbonized or heat-degraded during the polymerization reaction of the resin, and the odor of the wax can induce bad effects during the polymerization of the resin, the production of the toner or a printing process. Also, Korean Patent Laid Open No. 10-2005-0085116 discloses a resin to which a wax having substituent groups was dispersed, and a polyester resin reacted with a wax having substituent groups. However, in this case, the dispersibility of wax is not satisfactory, or the reacted wax does not fully perform its releasing effect during the toner fixing process. Also, in U.S. Pat. No. 7,226,984, the fixing property of a toner is improved by introducing carboxyl-modified polyolefin or hydroxyl-terminated polyalkadiene into the structure of the polyester resin.
Meanwhile, in preparing a polyester resin for toner, a catalyst such as germanium based catalyst, antimony based catalyst, and tin based catalyst and so on has been used. However, because the catalyst should be used in large amount due to a low catalytic activity of the catalyst, the catalyst is not desirable in an environmental aspect. The conventional catalyst deteriorates the transparency of a polyester resin due to its characteristic coloring property (for example, the antimony based catalyst has a gray coloring property). Therefore, titanium based catalyst is tried to improve the catalytic activity and the transparency of a polyester resin, and the titanium based catalyst includes tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, ethylacetoaceticester titanate, isostearyl titanate, titanium dioxide, TiO2/SiO2 co-precipitates, TiO2/ZrO2 co-precipitates, and so on.